Gamma-irradiation of exponentially-growing cultures of the radioresistant protozoan Tetrahymena leads to a transient, dose-dependent decrease in the polysome content. Both initiation and elongation (as measured by a new Modified Edman procedure) continue during the irradiation albeit at altered rates, but the protein synthesized is thereafter degraded prior to resumption of new protein synthesis. Ths response will be compared to those produced by other injuries, such as heat and UV-irradiation in both Tetrahymena and mammalian cells. In addition the proteins synthesized in the irradiated cells will be characterized by their behavior during electrophoresis and ion-exchange or DNA-affinity chromatography. Ribosomal RNA synthesis is severely inhibited in the irradiated cultures, while the processing of the reduced amounts of rRNA is not significantly affected. The reduction and recovery of rRNA synthesis will be correlated with possible nucleolar aggregation and re-amplification of ribosomal DNA. Total messenger-like RNA synthesis does not seem to be significantly depressed in irradiated cultures, but more detailed analyses of the actual species of mRNA synthesized post-irradiaton are in progress. Cellulose chromatography of poly A-containing RNA and competition hybridization are being used to determine if the same or different messages are synthesized and translated post-irradiation. BIBLIOGRAPHIC REFERENCES: Nancy L. Oleinick, "The Rate of Initiation Protein Synthesis in Intact Cells Measured by a Modified Edman Procedure", Fed. Proc. 34, 521 (1975, Abstract); Susan G. Ernest, Ronald C. Rustad, and Nancy L. Oleinick, "Post-Irradiation Modifications in RNA Synthesis in the Ciliate Protozoan Tetrahymena pyriformis", Radiat. Res. 62, 585 (1975, abstract).